In recent years, in conjunction with the development of computer graphics technology, image processing devices such as video game machines and simulation devices have widely and generally proliferated.
In particular, game devices of a form wherein a three-dimensional space in which multiple segments are positioned is captured from a prescribed visual point and displayed on a monitor as a projection on a two-dimensional screen have high product value. In interactive game devices called role playing games, for example, a player moves a specific segment (hereinafter called a model) in virtual space by moving an input device. This model approaches another segment (which represents a human being or a treasure chest; hereinafter called "(the) target") that is positioned in the virtual space, and communication takes place between the model and the target. By communication is meant, for example, a "conversation" being conducted in which the model and the target person talk to each other, or an interaction such as opening the target treasure chest. The question of whether or not communication has occurred is settled by a contact decision or the like in which a judgment is made as to whether or not there was contact between the model and the target.
In conventional role playing games, this has been done in virtual space defined in two dimensions. Because the virtual space is two-dimensional, the apparent distance between the model and the target on the display screen is the distance between the model and target in the game development, and a player can intuitively grasp the positional relationship between the two.
However, in game devices such as discussed in the foregoing, in which the positions of models and such are specified in three dimensions, it is possible to observe the models and targets as if they existed in the real world, and it is possible to have situations arise wherein the opponent is clearly discernable judging from the mutual positional relationship, even if there is no contact on the display screen. If, even in such cases as this, there is allowed to be no communication unless there is contact between the model and the target, as in conventional game devices defined in two dimensions, the sense of reality will be lacking, and the game will be made uninteresting. If we should hypothetically say that making contact is the condition of communication, then the following troubles arise.
Ordinarily, with game devices defined in three dimensions, a view-change visual point for observing the virtual space is established at some position separated from the visual point of the model. When an obstruction is positioned between the model and the target, although both the model and the target can be seen from the view-change visual point, the situation is one in which the target cannot be discerned from the visual point of the model. In such a case as this, that the model cannot move toward the target is obvious. It becomes necessary, therefore, either to have the model controlled such that it cannot move over or through the obstruction, or to have a display made showing that the model cannot approach the target.
Furthermore, when virtual space is defined in three dimensions, if the coordinates in the depth-dimension of the screen (the direction of the Z axis in the visual point coordinate system) are different, in cases, for example, where the model and target are observed from directly above the plane in the virtual space, even if there is a difference in the coordinate value (height) between the model and target, that difference will hardly appear at all on the display screen, and we can predict that it will then be very difficult to manipulate the model so that it approaches the target.
Also, even assuming that the model has been made to approach the target, the need arises to alter the way the model is oriented so that it faces the target.
In other words, in game devices where a perspective conversion is conducted to convert segments defined in three dimensions to two-dimensional coordinates in order to display them on a monitor, it is believed that various difficulties will arise, as noted above, when methods are adopted which are used in role playing games defined from the beginning in two dimensions.
On the other hand, in terms of a method for specifying a target in a game device defined in three dimensions, there is the publicly known technology of aim fixation (that is, capturing some target as the attack objective; hereinafter also referred to as "lock-on"), used, for example, in conventional game machines which simulate aerial combat.
Thus we can conceive of this technology being used such that a player locks on by overlapping the cursor on the target with which he or she desires to communicate.
However, such conventional game machines that simulate aerial combat simulate the aerial combat within a virtual space that imitates air, so it is presupposed that no obstruction exists between the enemy craft that is the target and one's own craft that is the model. For this reason, this type of game machine that simulates aerial combat does nothing more than judge whether or not the cursor has been overlapped on the enemy craft, and makes no judgment as to whether or not there is an obstruction hindering the attack.
That being so, in game devices wherein it is supposed that an obstruction may intrude between the model and the target, the said conventional lock-on technology cannot be employed as is.
Moreover, conventional lock-on technology is a simple display in which the cursor is merely fixed to a displayed object, making for visual images that lack variation.